<!DOCTYPE HTML>
<html lang="en" >
    
    <head>
        
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <title>第二节：定义变量 | 微信小程序</title>
        <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
        <meta name="description" content="">
        <meta name="generator" content="GitBook 2.6.7">
        
        
        <meta name="HandheldFriendly" content="true"/>
        <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
        <meta name="apple-mobile-web-app-capable" content="yes">
        <meta name="apple-mobile-web-app-status-bar-style" content="black">
        <link rel="apple-touch-icon-precomposed" sizes="152x152" href="../gitbook/images/apple-touch-icon-precomposed-152.png">
        <link rel="shortcut icon" href="../gitbook/images/favicon.ico" type="image/x-icon">
        
    <link rel="stylesheet" href="../gitbook/style.css">
    
        
        <link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-highlight/website.css">
        
    
        
        <link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-search/search.css">
        
    
        
        <link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-fontsettings/website.css">
        
    
    

        
    
    
    <link rel="next" href="../di-liu-zhang-ff1a-es6-yu-fa/di-san-jie-ff1a-han-shu.html" />
    
    
    <link rel="prev" href="../di-liu-zhang-ff1a-es6-yu-fa/di-yi-jie-ff1a-shi-yao-shi-es6-yu-fa.html" />
    

        
    </head>
    <body>
        
        
    <div class="book"
        data-level="5.2"
        data-chapter-title="第二节：定义变量"
        data-filepath="di-liu-zhang-ff1a-es6-yu-fa/di-er-jie-ff1a-es6-yu-fa.md"
        data-basepath=".."
        data-revision="Tue Feb 12 2019 17:48:38 GMT+0800 (中国标准时间)"
        data-innerlanguage="">
    

<div class="book-summary">
    <nav role="navigation">
        <ul class="summary">
            
            
            
            

            

            
    
        <li class="chapter " data-level="0" data-path="index.html">
            
                
                    <a href="../index.html">
                
                        <i class="fa fa-check"></i>
                        
                        Introduction
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="1" data-path="chapter1.html">
            
                
                    <a href="../chapter1.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>1.</b>
                        
                        第一章：小程序前奏
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.1" data-path="chapter1/di-yi-jie-ff1a-ren-shi-xiao-cheng-xu.html">
            
                
                    <a href="../chapter1/di-yi-jie-ff1a-ren-shi-xiao-cheng-xu.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>1.1.</b>
                        
                        第一节：认识小程序
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="1.2" data-path="chapter1/di-er-jie-ff1a-zhun-bei-gong-zuo.html">
            
                
                    <a href="../chapter1/di-er-jie-ff1a-zhun-bei-gong-zuo.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>1.2.</b>
                        
                        第二节：准备工作
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="1.3" data-path="chapter1/di-san-jie-ff1a-kai-fa-gong-ju-jie-shao.html">
            
                
                    <a href="../chapter1/di-san-jie-ff1a-kai-fa-gong-ju-jie-shao.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>1.3.</b>
                        
                        第三节：开发工具介绍
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="1.4" data-path="chapter1/di-liu-jie-ff1a-wxss-yu-fa.html">
            
                
                    <a href="../chapter1/di-liu-jie-ff1a-wxss-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>1.4.</b>
                        
                        第六节：WXSS语法
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.</b>
                        
                        第二章：小程序基础
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.1" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-yi-jie-ff1a-kuang-jia-jie-shao.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-yi-jie-ff1a-kuang-jia-jie-shao.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.1.</b>
                        
                        第一节：项目结构
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.2" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-er-jie-ff1a-wxml-yu-fa.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-er-jie-ff1a-wxml-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.2.</b>
                        
                        第二节：配置
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.3" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-san-jie-ff1a-wxml-yu-fa.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-san-jie-ff1a-wxml-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.3.</b>
                        
                        第三节：WXML语法
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.4" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-si-jie-ff1a-wxss-yu-fa.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-si-jie-ff1a-wxss-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.4.</b>
                        
                        第五节：事件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.5" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-liu-jie-ff1a-wxss-yu-fa.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-liu-jie-ff1a-wxss-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.5.</b>
                        
                        第六节：WXSS语法
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.6" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-qi-jie-ff1a-flex-bu-ju.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-qi-jie-ff1a-flex-bu-ju.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.6.</b>
                        
                        第七节：flex布局
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.7" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-bajie-ff1a-app-sheng-ming-zhou-qi.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-bajie-ff1a-app-sheng-ming-zhou-qi.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.7.</b>
                        
                        第八节：APP对象
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.8" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-jiu-jie-ff1a-page-dui-xiang.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-jiu-jie-ff1a-page-dui-xiang.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.8.</b>
                        
                        第九节：Page对象
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="2.9" data-path="di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-shi-zhang-ff1a-wxs-yu-fa.html">
            
                
                    <a href="../di-er-zhang-ff1a-kai-fa-zhun-bei-gong-zuo/di-shi-zhang-ff1a-wxs-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>2.9.</b>
                        
                        第十节：WXS语法
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3" data-path="di-san-zhang-ff1a-chang-yong-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.</b>
                        
                        第三章：常用组件
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.1" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-yi-jie-ff1a-shi-tu-rong-qi-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-yi-jie-ff1a-shi-tu-rong-qi-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.1.</b>
                        
                        第一节：scroll-view组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.2" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-er-jieff1a-swiper-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-er-jieff1a-swiper-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.2.</b>
                        
                        第二节：swiper组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.3" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-san-jie-ff1a-movable-view-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-san-jie-ff1a-movable-view-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.3.</b>
                        
                        第三节：movable-view组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.4" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-sijie-ff1a-icon-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-sijie-ff1a-icon-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.4.</b>
                        
                        第四节：icon组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.5" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-wu-jie-ff1a-text-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-wu-jie-ff1a-text-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.5.</b>
                        
                        第五节：text组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.6" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/di-liu-jie-ff1a-input-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/di-liu-jie-ff1a-input-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.6.</b>
                        
                        第六节：input组件
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="3.7" data-path="di-san-zhang-ff1a-chang-yong-zu-jian/zi-ding-yi-zu-jian.html">
            
                
                    <a href="../di-san-zhang-ff1a-chang-yong-zu-jian/zi-ding-yi-zu-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>3.7.</b>
                        
                        自定义组件
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="4" >
            
            <span><b>4.</b> 第四章：小程序API</span>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="4.1" data-path="di-yi-jie-ff1a-wang-luo-qing-qiu-api.html">
            
                
                    <a href="../di-yi-jie-ff1a-wang-luo-qing-qiu-api.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>4.1.</b>
                        
                        第一节：网络请求API
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="5" data-path="di-liu-zhang-ff1a-es6-yu-fa.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.</b>
                        
                        第五章：ES6语法
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="5.1" data-path="di-liu-zhang-ff1a-es6-yu-fa/di-yi-jie-ff1a-shi-yao-shi-es6-yu-fa.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-yi-jie-ff1a-shi-yao-shi-es6-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.1.</b>
                        
                        第一节：什么是ES6语法
                    </a>
            
            
        </li>
    
        <li class="chapter active" data-level="5.2" data-path="di-liu-zhang-ff1a-es6-yu-fa/di-er-jie-ff1a-es6-yu-fa.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-er-jie-ff1a-es6-yu-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.2.</b>
                        
                        第二节：定义变量
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.3" data-path="di-liu-zhang-ff1a-es6-yu-fa/di-san-jie-ff1a-han-shu.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-san-jie-ff1a-han-shu.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.3.</b>
                        
                        第三节：函数
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.4" data-path="di-liu-zhang-ff1a-es6-yu-fa/di-si-jie-ff1a-lei.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-si-jie-ff1a-lei.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.4.</b>
                        
                        第四节：类
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.5" data-path="di-liu-zhang-ff1a-es6-yu-fa/di-wu-jie-ff1a-mo-kuai.html">
            
                
                    <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-wu-jie-ff1a-mo-kuai.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.5.</b>
                        
                        第五节：模块
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="6" data-path="di-wu-zhang-ff1a-yun-kai-fa.html">
            
                
                    <a href="../di-wu-zhang-ff1a-yun-kai-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.</b>
                        
                        第六章：云开发
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="6.1" data-path="di-yi-jie-ff1a-shi-yao-shi-yun-kai-fa.html">
            
                
                    <a href="../di-yi-jie-ff1a-shi-yao-shi-yun-kai-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.1.</b>
                        
                        第一节：什么是云开发
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.2" data-path="di-er-jie-ff1a-zhu-ce-wei-xin-xiao-cheng-xu.html">
            
                
                    <a href="../di-er-jie-ff1a-zhu-ce-wei-xin-xiao-cheng-xu.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.2.</b>
                        
                        第二节：注册微信小程序
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.3" data-path="di-san-jie-ff1a-kai-tong-yun-kai-fa.html">
            
                
                    <a href="../di-san-jie-ff1a-kai-tong-yun-kai-fa.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.3.</b>
                        
                        第三节：开通云开发
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.4" data-path="di-si-jie-ff1a-shu-ju-ku.html">
            
                
                    <a href="../di-si-jie-ff1a-shu-ju-ku.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.4.</b>
                        
                        第四节：数据库准备
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.5" data-path="di-wu-jie-ff1a-shu-ju-ku-cao-zuo.html">
            
                
                    <a href="../di-wu-jie-ff1a-shu-ju-ku-cao-zuo.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.5.</b>
                        
                        第五节：数据库操作
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.6" data-path="di-liu-jie-ff1a-command-zhi-ling.html">
            
                
                    <a href="../di-liu-jie-ff1a-command-zhi-ling.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.6.</b>
                        
                        第六节：command指令
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.7" data-path="di-qi-jie-ff1a-gao-ji-cha-xun.html">
            
                
                    <a href="../di-qi-jie-ff1a-gao-ji-cha-xun.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.7.</b>
                        
                        第七节：高级查询
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.8" data-path="di-ba-jie-ff1a-wen-jian-shang-chuan.html">
            
                
                    <a href="../di-ba-jie-ff1a-wen-jian-shang-chuan.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.8.</b>
                        
                        第八节：文件操作
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.9" data-path="di-jiu-jie-ff1a-node-huan-jing-da-jian.html">
            
                
                    <a href="../di-jiu-jie-ff1a-node-huan-jing-da-jian.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.9.</b>
                        
                        第九节：node环境搭建
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.10" data-path="di-shi-jie-ff1a-yun-han-shu.html">
            
                
                    <a href="../di-shi-jie-ff1a-yun-han-shu.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.10.</b>
                        
                        第十节：云函数
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.11" data-path="di-shi-yi-jie-ff1a-yun-han-shu-jian-ce-nei-rong-an-quan.html">
            
                
                    <a href="../di-shi-yi-jie-ff1a-yun-han-shu-jian-ce-nei-rong-an-quan.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.11.</b>
                        
                        第十一节：检测内容安全
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.12" data-path="di-shi-er-jie-ff1a-yun-han-shu-tu-pian-jian-huang.html">
            
                
                    <a href="../di-shi-er-jie-ff1a-yun-han-shu-tu-pian-jian-huang.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.12.</b>
                        
                        第十二节：图片鉴黄
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.13" data-path="di-shi-san-jie-ff1a-yong-hu-shou-quan.html">
            
                
                    <a href="../di-shi-san-jie-ff1a-yong-hu-shou-quan.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.13.</b>
                        
                        第十三节：用户授权
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="6.14" data-path="di-shi-si-jie-ff1a-qi-ta-shou-quan-fang-shi.html">
            
                
                    <a href="../di-shi-si-jie-ff1a-qi-ta-shou-quan-fang-shi.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.14.</b>
                        
                        第十四节：其他授权方式
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    


            
            <li class="divider"></li>
            <li>
                <a href="https://www.gitbook.com" target="blank" class="gitbook-link">
                    Published with GitBook
                </a>
            </li>
            
        </ul>
    </nav>
</div>

    <div class="book-body">
        <div class="body-inner">
            <div class="book-header" role="navigation">
    <!-- Actions Left -->
    

    <!-- Title -->
    <h1>
        <i class="fa fa-circle-o-notch fa-spin"></i>
        <a href="../" >微信小程序</a>
    </h1>
</div>

            <div class="page-wrapper" tabindex="-1" role="main">
                <div class="page-inner">
                
                
                    <section class="normal" id="section-">
                    
                        <h1 id="es6&#x8BED;&#x6CD5;&#xFF1A;">ES6&#x8BED;&#x6CD5;&#xFF1A;</h1>
<p>&#x56E0;&#x4E3A;&#x672C;&#x8BFE;&#x7A0B;&#x4E0D;&#x662F;&#x4E13;&#x4E1A;&#x7684;&#x524D;&#x7AEF;&#x8BFE;&#x7A0B;&#xFF0C;&#x53EA;&#x662F;&#x4E3A;&#x4E86;&#x5FAE;&#x4FE1;&#x5C0F;&#x7A0B;&#x5E8F;&#x7684;&#x5B66;&#x4E60;&#x505A;&#x4E00;&#x4E9B;&#x94FA;&#x57AB;&#xFF0C;&#x6240;&#x4EE5;&#x53EA;&#x4ECB;&#x7ECD;&#x5230;&#x4E00;&#x4E9B;&#x5E38;&#x7528;&#x7684;&#x8BED;&#x6CD5;&#x3002;</p>
<h2 id="&#x5B9A;&#x4E49;&#x53D8;&#x91CF;&#x7684;&#x65B0;&#x5173;&#x952E;&#x5B57;&#xFF1A;">&#x5B9A;&#x4E49;&#x53D8;&#x91CF;&#x7684;&#x65B0;&#x5173;&#x952E;&#x5B57;&#xFF1A;</h2>
<h3 id="let&#xFF1A;">let&#xFF1A;</h3>
<p><code>let</code>&#x8DDF;<code>var</code>&#x4E00;&#x6837;&#xFF0C;&#x4E5F;&#x662F;&#x7528;&#x6765;&#x5B9A;&#x4E49;&#x53D8;&#x91CF;&#xFF0C;&#x4F46;&#x662F;&#x4ED6;&#x6BD4;<code>var</code>&#x66F4;&#x52A0;&#x7684;&#x5B89;&#x5168;&#xFF0C;&#x4F53;&#x73B0;&#x5728;&#x4EE5;&#x4E0B;&#x4E24;&#x70B9;&#xFF1A;</p>
<ol>
<li><p>&#x4E0D;&#x4F1A;&#x51FA;&#x73B0;&#x53D8;&#x91CF;&#x63D0;&#x5347;&#x7684;&#x60C5;&#x51B5;&#x3002;</p>
<pre><code class="lang-javascript"> <span class="hljs-built_in">console</span>.log(a);
 <span class="hljs-keyword">var</span> a = <span class="hljs-number">10</span>;
</code></pre>
<p>&#x6309;&#x9053;&#x7406;&#x53D8;&#x91CF;<code>a</code>&#x662F;&#x5728;&#x6253;&#x5370;&#x7684;&#x540E;&#x9762;&#x5B9A;&#x4E49;&#x7684;&#xFF0C;&#x4F46;&#x662F;&#x4EE5;&#x4E0A;&#x7684;&#x4EE3;&#x7801;&#x5E76;&#x4E0D;&#x4F1A;&#x51FA;&#x9519;&#xFF0C;&#x800C;&#x662F;&#x4F1A;&#x6253;&#x5370;<code>undefined</code>&#xFF0C;&#x56E0;&#x4E3A;<code>var</code>&#x4F1A;&#x628A;&#x53D8;&#x91CF;<code>a</code>&#x63D0;&#x5347;&#x5230;&#x4EE3;&#x7801;&#x6700;&#x5F00;&#x59CB;&#x7684;&#x5730;&#x65B9;&#x8FDB;&#x884C;&#x5B9A;&#x4E49;&#x3002;&#x4F46;&#x662F;&#x5982;&#x679C;&#x4F7F;&#x7528;<code>let</code>&#x5C31;&#x4E0D;&#x4F1A;&#x51FA;&#x73B0;&#x8FD9;&#x79CD;&#x95EE;&#x9898;&#x4E86;&#x3002;</p>
<pre><code class="lang-js"> <span class="hljs-built_in">console</span>.log(b);
 <span class="hljs-keyword">let</span> b = <span class="hljs-number">10</span>;
</code></pre>
<p>&#x6B64;&#x65F6;&#x518D;&#x53BB;&#x6253;&#x5370;&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x5C31;&#x76F4;&#x63A5;&#x4F1A;&#x629B;&#x51FA;&#x4E00;&#x4E2A;&#x9519;&#x8BEF;<code>ReferenceError: b is not defined.</code>&#xFF0C;&#x8FD9;&#x624D;&#x662F;&#x6B63;&#x786E;&#x7684;&#x65B9;&#x5F0F;&#x3002;<br><strong>&#x6CE8;&#x610F;&#xFF1A;&#x5C0F;&#x7A0B;&#x5E8F;&#x4E2D;&#x4E0D;&#x80FD;&#x771F;&#x6B63;&#x89E3;&#x6790;ES6&#x8BED;&#x6CD5;&#xFF0C;&#x4ED6;&#x53EA;&#x662F;&#x501F;&#x52A9;&#x4E86;&#x7B2C;&#x4E09;&#x65B9;&#x5DE5;&#x5177;&#x5C06;ES6&#x8BED;&#x6CD5;&#x8F6C;&#x6210;ES5&#x8BED;&#x6CD5;&#x8FD0;&#x884C;&#x7684;&#xFF0C;&#x5728;&#x5E95;&#x5C42;&#x4E5F;&#x662F;&#x7528;var&#x6765;&#x4EE3;&#x66FF;let&#x7684;&#xFF0C;&#x6240;&#x4EE5;&#x4F9D;&#x7136;&#x4F1A;&#x53D1;&#x751F;&#x53D8;&#x91CF;&#x63D0;&#x5347;&#x3002;</strong></p>
</li>
<li><p>&#x53EA;&#x5728;&#x5F53;&#x524D;&#x4EE3;&#x7801;&#x5757;&#x5185;&#x6709;&#x6548;&#x3002;</p>
<pre><code class="lang-js"> <span class="hljs-keyword">for</span>(<span class="hljs-keyword">var</span> i=<span class="hljs-number">0</span>;i&lt;=<span class="hljs-number">3</span>;i++){
     <span class="hljs-built_in">console</span>.log(i);
 }
 <span class="hljs-built_in">console</span>.log(i);
</code></pre>
<p>&#x6309;&#x9053;&#x7406;&#x6765;&#x8BF4;<code>i</code>&#x5728;<code>for</code>&#x5FAA;&#x73AF;&#x7ED3;&#x675F;&#x540E;&#xFF0C;&#x5E94;&#x8BE5;&#x5C31;&#x4E0D;&#x80FD;&#x591F;&#x518D;&#x4F7F;&#x7528;&#x4E86;&#xFF0C;&#x4F46;&#x662F;&#x6211;&#x4EEC;&#x4E0B;&#x9762;&#x518D;&#x6253;&#x5370;<code>i</code>&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x4F1A;&#x53D1;&#x73B0;&#x6253;&#x5370;&#x7684;&#x7ED3;&#x679C;&#x662F;<code>3</code>&#x800C;&#x4E0D;&#x662F;&#x629B;&#x51FA;&#x5F02;&#x5E38;&#xFF0C;&#x8FD9;&#x5728;&#x4E00;&#x4E9B;&#x60C5;&#x51B5;&#x4E0B;&#x4E5F;&#x4F1A;&#x4EA7;&#x751F;&#x83AB;&#x540D;&#x5176;&#x5999;&#x7684;&#x9519;&#x8BEF;&#x3002;&#x4F46;&#x662F;<code>let</code>&#x5C31;&#x4E0D;&#x4F1A;&#x51FA;&#x73B0;&#x8FD9;&#x79CD;&#x60C5;&#x51B5;&#x4E86;&#x3002;&#x793A;&#x4F8B;&#x4EE3;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre><code class="lang-js"> <span class="hljs-keyword">for</span>(<span class="hljs-keyword">let</span> i=<span class="hljs-number">0</span>; i&lt;=<span class="hljs-number">3</span>; i++){
     <span class="hljs-built_in">console</span>.log(i);
 }
 <span class="hljs-built_in">console</span>.log(i);
</code></pre>
<p>&#x6B64;&#x65F6;&#x518D;&#x6253;&#x5370;<code>i</code>&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x5C31;&#x4F1A;&#x629B;&#x51FA;&#x9519;&#x8BEF;<code>ReferenceError: b is not defined.</code>&#x3002;</p>
</li>
</ol>
<h3 id="const&#xFF1A;">const&#xFF1A;</h3>
<p><code>const</code>&#x662F;&#x7528;&#x6765;&#x5B9A;&#x4E49;&#x5E38;&#x91CF;&#x7684;&#xFF0C;&#x5E38;&#x91CF;&#x662F;&#x4E00;&#x65E6;&#x5B9A;&#x4E49;&#x597D;&#x4E86;&#x4EE5;&#x540E;&#xFF0C;&#x5C31;&#x4E0D;&#x80FD;&#x591F;&#x518D;&#x4FEE;&#x6539;&#x4E86;&#x3002;&#x6BD4;&#x5982;&#x4EE5;&#x4E0B;&#x4EE3;&#x7801;&#xFF1A;</p>
<pre><code class="lang-js"><span class="hljs-keyword">const</span> PI = <span class="hljs-number">3.14</span>;
PI = <span class="hljs-number">3</span> <span class="hljs-comment">// &#x4F1A;&#x629B;&#x51FA;&#x5F02;&#x5E38;</span>
</code></pre>
<p><code>const</code>&#x53EA;&#x662F;&#x7528;&#x6765;&#x9650;&#x5236;&#x6307;&#x5411;&#x7684;&#x5185;&#x5B58;&#x5730;&#x5740;&#x4E0D;&#x80FD;&#x6539;&#x53D8;&#xFF0C;&#x4F46;&#x662F;&#x5982;&#x679C;&#x8FD9;&#x4E2A;&#x5185;&#x5B58;&#x5730;&#x5740;&#x4E0A;&#x7684;&#x6570;&#x636E;&#x6539;&#x53D8;&#x4E86;&#xFF0C;&#x662F;&#x53EF;&#x4EE5;&#x7684;&#x3002;&#x6216;&#x8005;&#x8BF4;&#x5F97;&#x76F4;&#x767D;&#x4E00;&#x70B9;&#xFF0C;&#x5C31;&#x662F;&#x6307;&#x5411;&#x7684;&#x5982;&#x679C;&#x662F;&#x4E00;&#x4E2A;&#x53EF;&#x53D8;&#x7684;&#x5BB9;&#x5668;&#xFF0C;&#x5BB9;&#x5668;&#x4E2D;&#x7684;&#x6570;&#x636E;&#x6539;&#x53D8;&#x4E86;&#xFF0C;&#x90A3;&#x4E48;&#x662F;&#x5141;&#x8BB8;&#x7684;&#x3002;&#x6BD4;&#x5982;&#x4EE5;&#x4E0B;&#x4EE3;&#x7801;&#xFF1A;</p>
<pre><code class="lang-js"><span class="hljs-keyword">const</span> mylist = [<span class="hljs-number">1</span>,<span class="hljs-number">2</span>,<span class="hljs-number">3</span>];
mylist.push(<span class="hljs-number">4</span>);
<span class="hljs-built_in">console</span>.log(mylist);
</code></pre>
<p>&#x4EE5;&#x4E0A;&#x4EE3;&#x7801;&#x540E;&#x9762;&#x4F1A;&#x6253;&#x5370;&#x4E00;&#x4E2A;<code>[1,2,3,4]</code>&#x7684;&#x6570;&#x7EC4;&#x3002;</p>
<hr>

                    
                    </section>
                
                
                </div>
            </div>
        </div>

        
        <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-yi-jie-ff1a-shi-yao-shi-es6-yu-fa.html" class="navigation navigation-prev " aria-label="Previous page: 第一节：什么是ES6语法"><i class="fa fa-angle-left"></i></a>
        
        
        <a href="../di-liu-zhang-ff1a-es6-yu-fa/di-san-jie-ff1a-han-shu.html" class="navigation navigation-next " aria-label="Next page: 第三节：函数"><i class="fa fa-angle-right"></i></a>
        
    </div>
</div>

        
<script src="../gitbook/app.js"></script>

    
    <script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
    

    
    <script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
    

    
    <script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
    

    
    <script src="../gitbook/plugins/gitbook-plugin-fontsettings/buttons.js"></script>
    

<script>
require(["gitbook"], function(gitbook) {
    var config = {"highlight":{},"search":{"maxIndexSize":1000000},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
    gitbook.start(config);
});
</script>

        
    </body>
    
</html>
